1. Field of the Invention
The invention relates to the field of the measurement of gas emissions of the NOx type, in particular in industrial processes.
2. Related Art
Numerous industrial processes are based on the combustion of various fuels such as natural gas, LPG etc. Among these processes may be cited in particular second-melt smelting processes or those employed in furnaces for the melting of glass.
The oxidant for these processes, traditionally air, can be enriched with oxygen or even, in certain cases, replaced by oxygen. These processes produce in particular gases such as NOx compounds. The formation of these compounds depends on numerous parameters, which themselves depend on the process (nature of the charge, composition of the oxidant and fuel fluids, burner, pressure of the furnace, etc.).
Ever stricter standards are imposed as regards concern for the environment.
Continuous measurement of these compounds would allow better control of the processes from which they emanate, and/or would make it possible to minimize releases or emissions of NOx so as to comply as far as possible with the standards imposed.
The known methods of measurement can be grouped into two categories: on the one hand in situ measurements, by an appropriate NOx physical sensor and, on the other hand, measurements or estimates by software sensor.
In the example of processes which are conducted in a furnace, the smoke exiting the furnace is often at high temperatures (between 1400° C. and 1600° C.) and is laden with dust. All these conditions therefore affect the operation of the NOx physical sensors which may be installed at the exit of a furnace.
In order to reduce the overly high temperatures of the smoke, recourse is had to a gas conditioning procedure.
Furthermore, measurements made by a physical sensor require frequent calibration as well as technical monitoring of the sensor.
Physical sensors, which are in themselves expensive, are therefore unsuitable for continuous tracking at reasonable cost.
Software sensors are also known, but they do not currently make it possible to attain high accuracy.
In particular, a relative error of estimation of the order of 70% is obtained, which is too large for current needs.
Furthermore, such a sensor requires, in practice, a considerable number of inputs (around 14) and therefore utilizes this many physical sensors to acquire these data. This results in considerable noise in the input data.
Hence, the problem arises of finding a novel process and a novel device for measuring oxides of nitrogen (NOx) in smoke, especially at the furnace exit.
The problem also arises of finding a process and a device giving reliable information regarding the concentration of oxides of nitrogen (NOx) in smoke without performing a direct physical measurement of these oxides of nitrogen.
The problem also arises of finding a sensor allowing continuous measurement, in a reliable manner and with industry-acceptable maintenance, of the emissions of NOx in smoke, in particular at the furnace exit.
The problem furthermore arises of finding a sensor of software type not requiring too large a number of input data.